PEX™ plumbing (or crosslinked polyethylene) is part of a water supply piping system that has several advantages over metal pipe (copper, iron, lead) or rigid plastic pipe (PVC, CPVC, ABS) systems. It is flexible, resistant to scale and chlorine, doesn't corrode or develop pinholes, is faster to install than metal or rigid plastic, and has fewer connections and fittings.
PEX™ tubing is made from crosslinked HDPE (high density polyethylene) polymer. The HDPE is melted and continuously extruded into tube. The crosslinking of the HDPE is accomplished in one of three different methods.
PEX™ plumbing has been in use in Europe since about 1970, and was introduced in U.S.A. around 1980. The use of PEX™ has been increasing ever since, replacing copper pipe in many applications, especially radiant heating systems installed in the slab under floors or walkways. Interest in PEX™ for hot and cold water plumbing has increased recently in the United States.
Flexible PEX™ tube is manufactured by extrusion, and shipped and stored on spools, where rigid plastic or metal piping must be cut to some practical length for shipping and storage. This leads to several advantages, including lower shipping and handling costs due to decreased weight and improved storage options.
PEX™ plumbing installations require fewer fittings than rigid piping. The flexible tubing can turn 90 degree corners without the need for elbow fittings, and PEX™ tubing unrolled from spools can be installed in long runs without the need for coupling fittings.
The terms PEX™ pipe and PEX™ tube have been used by persons of skill in the art interchangeably, however some manufacturers distinguish between the two by manufacturing to different inside/outside diameters. The term PEX™ tubing when used herein is intended to refer generally to either PEX™ pipe or PEX™ tube.
Some applications require PEX™ with added oxygen barrier properties. Radiant floor heating (or hydronic heating systems) may include some ferrous (iron-containing) components which will corrode over time if exposed to oxygen. Since standard PEX™ tubing allows some oxygen to penetrate through the tube walls, various “Oxygen Barrier PEX™” tubing has been designed to prevent diffusion of oxygen into these systems.
As with PEX™ Tubing Corrugated Stainless Steel Tubing (CSST) is growing in popularity, and like PEX™ tubing is being used in both new construction and renovations of older buildings. Although the cost of this material is higher than regular pipe, the ease of installation, lack of joints and labour cots is making this material more attractive to the consumer. Once again like PEX™ tubing, this tubing is shipped in round coils or spools, and can become very difficult to push through joist and wall spaces. Corrugated Stainless Steel Tubing comes in many trade names, here is a few of them: Tracpipe™, Pro-Flex™ and Gastite™.
It is common during new construction and during renovations of buildings to use PEX™ Tubing to transmit domestic and heating, hot and cold water, from fixture to fixture. PEX™ Tubing is an excellent product for this purpose and its use is growing in popularity every year. The application we are interested is its flexibility and ability to be installed from fixture to fixture in continuously without or using only a few fittings. Due to this flexibility, the PEX™ Tubing has the ability to be inserted continuously through both large and small wall and floor cavities even ones filled with insulation.
The problem that does arise with PEX™ Tubing due to its continuous nature and requirement to be stored on rolls, is that this storage method causes the tubing to form a curvature. In essence this means the tubing, in it's natural state, is not straight like pipe. When attempting to straighten this PEX™ Tubing it just returns to its natural curvature. When this PEX™ Tubing is inserted into a wall or floor cavity, it is not straight but rather curved making this extremely difficult to line up. The PEX™ Tubing end is generally pointed away from the other side of the wall cavity where there is a hole or a point on the opposite wall the PEX™ Tubing is to go to or through.